Nansihu Lake,  composed of Weishanhu Lake, Zhaoyanghu Lake, Nanyanghu Lake and Dushanhu Lake, is the largest lake in North China. In this paper some environmental indexes of sediments from Nansihu Lake, such as lithology, sedimentation rate, magnetic susceptibility, TOC(total organic carbon), TN(total nitrogen), C/N and fossil pigment, were analyzed. The study shows that sedimentary difference between north and south Nansihu Lake occurred at 0.62 ka BP. Before 2.45 ka BP, fossil pigment was not found in sediments, and C/N was obviously high and even reached 60～80, characteristic of fluvial facies. The period from 2.45～1.3 ka BP was the period of forming Nansihu, reflected by abrupt increase of pigment content, and  corresponding change of other environmental indexes. Nansihu Lake was stable during 1.3 ka BP to 0.62 ka BP. After 0.62 ka BP, Dushanhu Lake in the north of Nansihu Lake was more like a river, while Weishanhu Lake in the south was a lake. Sedimentary characteristics showed above will be the basis of reconstructing the evolution history of Nansihu Lake, determining the level and scope of influence of the Yellow River flooding in this area and investigating the intensity of human activity in this area.